Have you ever lied on the remaining air left in your bottle? I know this may seem incredible for some but i've heard many of my friends admit that they already had lied about it at a moment or another
I've never lied about that, even if you do, when the DM fills up your tank after you've left, they'll know. And if you are lying to them underwater, you are risking your life, never good to do that.
why would people want to lie about that in the first place is the first question that comes to my mind while reading the question? For the danger or i don't know what???